Cellular mobile radio or cellular telephone systems have been developed for mobile communications. Typically, the planned service area is divided into a number of geographical areas or cells. The available frequency channels for the service area are divided among the cells. A cellular telephone communicates with a nearby cell base station via one of the several radio frequency channels assigned to the cell. Conventional circuits link the base station to the mobile telecommunications switching office, which switches calls between the cellular telephone system and the rest of the telephone network.
Current cellular telephones gain access to the base station, by transmitting to the base station a series of numbers or characters, specific to the cellular telephone being used. The numbers or characters represent the telephone number of the cellular telephone being used and the manufacturer's electronic serial number of the cellular telephone being used. The foregoing characters and numbers are checked at the base station to determine if the cellular telephone being used is allowed to use the base station selected and that the telephone number of the cellular telephone being used has the correct manufactures electronic serial number. If the telephone number and manufacturer's electronic serial number are found to be correct, the base station may further determine if the time elapsed and distance traveled by the cellular telephone from the last cellular telephone call are feasible. If, the cellular telephone traveled a feasible distance in the time elapsed from the last telephone call, the cellular telephone will be connected to the telephone network.
Unfortunately, people using off the shelf electronic receiving equipment are able to intercept and determine the telephone number and manufacturer's electronic serial number of cellular telephones, while the telephone number and manufacturer's electronic serial number are being transmitted at specific radio frequencies to the base station. During, 1993 United States Cellular Telephone companies lost approximately three hundred ninety four million dollars ($394,000,000.00) from the unauthorized use of cellular telephone numbers and manufacturers electronic serial numbers. It was estimated that the unauthorized use of cellular telephones cost United States Cellular telephone companies six hundred million dollars ($600,000,000.00) during 1994. If nothing is done to prevent the unauthorized use of cellular telephones, the above figure is expected to be higher each successive year.
Cellular telecommunications systems that utilize encryption and employ encrypted seed number signals have been developed to make it more difficult to make unauthorized cellular telephone calls. One of the difficulties with prior art encrypted cellular telecommunications systems is that encrypted seed number signals are generated in the cellular telephone and the data center that is used by the specific cellular telephone. In addition synchronization must be maintained between the cellular telephone and data center. If, the user of the cellular telephone traveled outside of the area of the data center and made a telephone call, i.e. in a different state, the data center in the different state would probably not know the encrypted seed number signal. The reason for the above is that the data center in the traveled to state would not be in synchronization with the cellular telephone and would probably be unable to determine the encrypted seed number. Furthermore, when the cellular telephone user returned to use the data center in the state that was traveled from, the original data center would be out of synchronization with the cellular telephone. The data centers in different states would have to know the call history of each cellular telephone in order to determine the encrypted seed number. The foregoing would involve a large amount of communications between data centers that may be owned by different entities.